1. Field of the Invention
The present invention relates to charging mechanisms for batteries and in particular to recharging batteries which must be substantially discharged before recharging.
2. Description of the Prior Art
A growing number of "cordless" or "mobile" electronic devices rely on rechargeable batteries rather than disposable batteries, including wireless telephones, laptops, personal digital assistants (PDAs), cordless telephones, etc. The devices typically utilize battery power when not connected to another power source, and recharge the battery when connected to an external power source through a charging cradle, power adapter, or the like.
In order to maximize useful lifetime, nickel-cadmium (NiCad) rechargeable batteries must be substantially discharged before being recharged. Although generally less expensive than "memory-free" rechargeable batteries such as nickel metal hydride (NiMH) or lithium ion (Li-Ion) batteries, the need for discharge prior to recharging has resulted in NiCad batteries finding less commercial acceptance than might be expected. A probable cause of this unpopularity is the hassle of trying to remember whether a battery has been discharged, or waiting until the battery has been discharged, before recharging.
Various charging schemes have been proposed for NiCad rechargeable batteries, each of which have proven less than satisfactory. For example, "flash" discharge mechanisms designed to quickly discharge a battery to an acceptable level before recharging have reduced the wait before a battery may be recharged, but can be only somewhat less harmful to battery life than recharging before complete discharge. Battery life is best when the battery is discharged utilizing a slow, controlled drain through a load.
It would be desirable, therefore, to provide a power management system for rechargeable batteries which intelligently controls discharge and recharging to extend battery life.